Various types of drill strings are deployed in a borehole for exploration and production of hydrocarbons and CO2 sequestration. A drill string generally includes drill pipe, a bottom hole assembly (BHA), and a drill bit that is rotated by a drill motor (mud motor) and/or the drill string itself. The BHA contains drill collars, which may be instrumented, and can be used to obtain measurements-while-drilling (MWD) or while-logging (LWD), for example.
Some drill strings can include components that allow the borehole to be drilled in directions other than vertical. Such drilling is referred to in the industry as “directional drilling.” While deployed in the borehole, the drill string may be subject to a variety of forces or loads. Because the drill string is in the borehole, the loads are unseen and can affect the dynamic behavior and direction of travel of the drill string.
To measure the loads/forces that affect dynamic behavior and behavior of a drill string, a number of downhole devices are placed in close proximity to the drill bit. Such devices typically include sensors for measuring downhole temperature and pressure, azimuth and inclination measuring devices and sensors that measure the acceleration of the BHA in different directions and the bending moment. The latter data can be used to characterize the drilling dynamics of the BHA, which depends on formation properties, the drill bit and the BHA configuration. In addition, based on measurements made by the MWD or other tools, rate of penetration (ROP), bit revolutions per minute (RPM), average or mean downhole weight on bit (WOB) and average or mean downhole torque on the bit (TOR) can be derived or measured directly. All of the above measurements, and others, fall into the broad category of “drilling parameters.”
Additionally, LWD and MWD instruments are frequently attached to the drill string to determine the formation geology and formation fluid conditions during the drilling operations. For instance, these devices can be used for identifying and evaluating rock formations and may be referred to as a “formation parameters” herein. It shall be understood that the formation parameters can be included within the category of drilling parameters.
As drilling parameters change, the immediate result of the unseen loads may be unknown. If the loads are detrimental, then continued operation of the drill string might cause damage or unreliable operation. In addition, the loads can cause either unexpected or undesirable deviations of the drilling trajectory.
One approach to predicting drilling trajectory is to produce models that take into account one or more combinations of drilling parameters. Such models can, in some cases, become so large and require extensive computational power. In some cases, the computation can become so extensive that the models are not practical for use in “real-time” situations.